The invention relates to a method of and an arrangement for burning a liquid or gaseous fuel in the presence of air or another oxidizer, and including introduction of water in a combustion chamber of an internal combustion engine, especially a reciprocating or rotary piston engine.
Conventional internal combustion engines, especially reciprocating piston engines with applied ignition, such as used in motor vehicles and stationary plants have a maximum thermal efficiency of approximately 30%. Thus the ratio of the energy value of the fuel supplied to the combustion chamber as compared to the energy which lastly is available, is no more than approximately 30%. Turbines, rotary piston engines, and the like are characterized by a similar low degree of efficiency.
It is known, in general, that the efficiency of internal combustion engines of the kind mentioned is increased by introducing water and other non-fuels into the combustion chamber, and in this context three different kinds of water addition are shown in the prior art and believed to be advantageous, namely:
(1) direct injection of water into the combustion chamber (for example DE-A-3 432 787 or U.S. Pat. No. 4,408,573);
(2) introduction of vapor or air of high humidity into the intake passage upstream of the combustion chamber (for example U.S. Pat. No. 4,479,907 or DE-A-2 602 287); and
(3) formation of a fuel-water emulsion which is introduced into the combustion chamber (for example DE-A-3 236 233 or U.S. Pat. No. 4,412,512).
These known systems all work in response to one or more operating parameters, usually in dependence on the number of revolutions of the internal combustion engine (for example U.S. Pat. No. 4,191,134), the negative pressure prevailing in the intake passage (for example U.S. Pat. No. 4,240,380), a knocking or pinging sensor (for example U.S. Pat. No. 4,406,255), the exhaust gas pressure (for example U.S. Pat. No. 4,191,134), and/or the temperature prevailing in the intake passage (EP-A-0 009 779). All of these systems afford more or less improvement of the efficiency while at the same time reducing the emission of ecologically damaging exhaust gases, and particularly reducing CO and NO.sub.x. The improvement in efficiency with the known structures should be about 10 to 15%, and this is quite remarkable. Furthermore, fuel consumption can be reduced by up to 50% (U.S. Pat. No. 4,479,907).
In order to further increase the efficiency and reduce the fuel consumption, it was also proposed by others to inject water directly into the combustion chamber in the range of the compressed fuel-air mixture and in front of the flame front during the combustion, i.e. after ignition of the fuel-air mixture but before autoignition of the final gas (cf. DE-A-3 133 939). This is intended to keep the temperature in the combustion chamber reliably below the "uncontrolled" or critical detonation or "knocking" temperature at higher compression ratios which are in the order of up to 18.7:1.
Starting from the very diverse state of the art mentioned, the inventors have invented a method and an arrangement of introducing the water which establishes an extremely smooth combustion even at the lowest speeds of the internal combustion engine, at higher efficiency and fuel savings which can reach approximately 60 to 65% and with a remarkable reduction of harmful substances, especially when using low octane fuel, such as regular gasoline or fuel of octane number "0", such as acetylene and the like.
The nucleus of the instant invention resides in the preparation and introduction of the fuel/water/air mixture into a combustion chamber while compressing and igniting the same such that an "initial or primary combustion" of the fuel/air mixture results at a temperature just below the uncontrolled or critical (head) temperature T.sub.c (knocking limit). The combustion with the present invention releases a correspondingly progressive "secondary combustion" of the admixed water. The "primary cycle" and the "secondary cycle" take place at each point of the combustion, in other words at each location of the flame front, in contrast to the solution according to DE-A-3 133 939. In contrast to the system known from this publication, and in accordance with the invention, a "primary combustion" occurs near the uncontrolled or critical temperature in the combustion chamber and is controlled by corresponding admixing of water. Up to now those skilled in the art were striving to produce combustion at the greatest possible temperature which is spaced from the critical temperature in the combustion chamber in order to positively prevent knocking or pinging of the internal combustion engine. It is for this reason that high octane fuels are used in high compression internal combustion engines for motor vehicles although they are required only in critical load ranges, and whereas the engines otherwise could operate on regular gasoline. However, sufficient reliability prevention of detonations at almost any operating condition is obtained by the use of high octane fuel (premium gasoline). In accordance with the present invention, the combustion occurs just below the detonation temperature limit at every operating condition, the peak temperature in the combustion chamber being kept just below the uncontrolled or critical temperature by the controlled admission of water at every operative state or working condition. Thus a temperature is controlled in the combustion chamber which is 1 to 5% below the critical temperature. This depends on the fuel used as well as the critical compression ratio or the critical pressure. It has been found that in applying the system according to the invention, the internal combustion engine can be run just below the detonation limit at every operative state or working condition, with "realistic" compression ratios .rho. (fuel/air) of up to 25:1.
In accordance with the method of the invention and in applying the arrangement according to the invention, surprisingly, highly explosive gases, such as acetylene may be burned without any difficulty in an internal combustion engine having a quasi-closed combustion chamber, as will be explained below with reference to an embodiment using a 1200 cm.sup.3 Austin engine for motor vehicles.
The combustion efficiency may be increased by up to 70% as compared to conventional internal combustion engines of the kind mentioned about when applying the method according to the invention or the arrangement according to the invention. The fuel consumption can be reduced by up to 65%. Also, the emission of CO and NO.sub.x is reduced to a minimum. The internal combustion engine is suitable above all for burning lead free gasoline. However, it should be stressed once again that the values mentioned can be obtained only if the "primary combustion" takes place just below the detonation temperature. The "secondary cycle" thus released at every locus of combustion continues the "primary cycle" such that on the whole a progressively "smooth" combustion is obtained. The "secondary cycle" so to speak causes dampening of the "initial or primary combustion" which takes place just below the knocking limit.
It is of great importance that the fuel, air or other oxidizing agent and water are mixed intensively before being introduced into the combustion chamber in order to achieve the "two-phase" combustion aimed at by the invention. With intensive mixing, the combustion takes place in the manner specified at each locus or place of combustion. To this end, a kind of mixing chamber is preferably formed in the intake passage before or upstream of the throttle flap which is usually provided. This mixing chamber, for instance, may be defined on the one hand by the air inlet opening and, on the other hand, by a constriction (venturi section) of the intake passage located upstream of the throttle flap. In this mixing chamber great turbulence of fuel, air, and water is created in order to achieve the desired thorough mixing of these three components.
The supply of water preferably takes place by injection into the mixing chamber mentioned, in response to the temperature prevailing in the combustion chamber, the injection of the water being effected at a temperature which is approximately from 1 to 5% below the critical temperature T.sub.c. The "primary combustion" should take place just below the critical temperature in all operating conditions, possibly 1 to 2% below the critical temperature. The injection of water is metered accordingly.
Provision is made for an additional introduction of water into the mixing chamber mentioned under the control of negative pressure in the suction passage, the injection of water explained above being superposed over this additional introduction. The introduction of water caused by negative pressure in the suction passage is sufficient for bringing the "primary combustion" close to the critical temperature T.sub.c in uncritical phases of operation.
Surprisingly, it has also been found that highly explosive acetylene (C.sub.2 H.sub.2) can be burned in accordance with the method of the invention without posing any risk and at extremely low consumption. In a test run with a 1200 cm.sup.3 Austin engine, the following values of consumption were recorded:
Running time: 10 minutes PA0 Rotational speed: 3000 r.p.m. PA0 Consumption of C.sub.2 H.sub.2 : 0.35 kg PA0 Consumption of H.sub.2 O: 2.8 kg.
The ratio of water to acetylene during this test thus was 8:1. There was also minimum emission of harmful substances during this test. In the combustion chamber, a temperature just below the critical temperature was maintained for the primary combustion of fuel (acetylene) and air. In the test the delivery of the water injection pump was constant during the injection phase. Of course, it is conceivable to render the delivery of the water injection pump variable in response to the temperature detected in the combustion chamber. The closer the temperature in the combustion chamber approaches the critical temperature, the greater the delivery of the water injection pump would have to be.
The external cooling of the combustion chamber is also significant. To this end, another temperature sensor (thermocouple) is provided at the water jacket surrounding the combustion chamber and coupled with the control unit for the cooling water pump.
The method according to the invention permits the combustion to be carried out at a "realistic" compression ratio of up to 25:1. The "realistic" compression ratio is defined as the volume of the fuel and oxidizer (air) alone. Such high "realistic" compression ratios are not possible with conventional internal combustion engines.
The water admixed to the fuel/air mixture in part may be recovered from the exhaust gases by known evaporation and condensation methods (cf. for example DE-C-3 102 088 or U.S. Pat. No. 4,279,223).
Of course, when applying the system according to the invention, the other engine parameters must be adapted accordingly. Specifically, it has been found that the ignition timing must be displaced closer to the upper dead center, with simultaneous earlier opening before the upper dead center position and a much later closing of the inlet valve after the lower dead center position. The "overlapping" thus is increased in order to obtain a good filling and flushing of the combustion chamber.
Apart from the temperature sensors described above, detonation or knocking sensors and/or pressure sensors may be provided for detecting the pressure in the combustion chamber to control the pressurized water injection and/or the external cooling agent pump. Although the use of detonation sensors is known, it has proved to be too inaccurate and not specific of the combustion. Above all, such detection sensors do not permit control of the initial primary combustion close to the detonation limit because the detonation limit is usually reached or surpassed before the detonation sensors respond.
For the structural design, reference should be made to the configuration of the water nozzle or nozzles embodied by a mouthpiece having a plurality of fine bores. Preferably the bores in the mouthpiece of the water nozzles are directed in the direction of flow and/or inclined with respect to the radial line of the mouthpiece so as to impress turbulences and an eddy current on the exiting water jets while, at the same time, vaporizing the same, whereby a contribution is made to the intimate mixing with fuel and air. Furthermore, turbulators in the form of guiding noses and the like may be associated with the fuel nozzle and/or the water nozzle(s).
If acetylene is used as fuel, at least one other fuel inlet is provided downstream of the throttle flap and opens into the intake passage, particularly the intake manifold. Moreover, a heat exchanger and/or a gas pressure regulator is preferably connected upstream of the fuel inlet. The heat exchanger mainly serves to preheat the gas as it expands in the intake passage or in the mixing chamber thereof so as to compensate for the temperature drop which occurs upon expansion and to prevent icing in the suction range.
When applying the system according to the invention, the exhaust gases have a rather low temperature, at any rate a substantially lower temperature than the exhaust gases of conventional internal combustion engines. For this reason, the magnitude of the exhaust gas temperature may be used as another control signal for controlling the injection of water, by corresponding provision of a thermocouple or temperature sensor to sense such temperature.
Finally, for especially critical operating phases injection of water may be coupled with the control of the throttle flap. In the phase, an additional manual control is provided over the temperature responsive control of the injection of the water.